This invention relates to a vane compressor adapted for compressing a refrigerant in air conditioners for automotive vehicles, and more particularly to a variable capacity vane compressor which is capable of changing its capacity by changing the timing of commencement of compression.
Conventional variable capacity vane compressors of this kind include one proposed, e.g. by Japanese Provisional Patent Publication (Kokai) No. 64-36997, which comprises a cylinder with its open ends closed by a pair of side blocks, and a rotor rotatably received within the cylinder, and a control element rotatable about its own axis in opposite directions for controlling the timing of commencement of compression.
The control element has one side surface thereof formed integrally with a pair of pressure-receiving protuberances projected therefrom at diametrically opposite locations. On the other hand, one of the side blocks has an end face thereof facing the rotor and formed therein with an annular recess, in which the control element is rotatably received, with each of the pressure-receiving protuberance dividing a pressure working space defined between the annular recess and the control element into a low pressure chamber and a high pressure chamber. Sealing means is mounted on the control element and fitted around required portions thereof including the pressure-receiving protuberances.
As shown in FIG. 1, the sealing means comprises a resilient sealing member (not shown) directly fitted around the control element, and an auxiliary sealing member which is formed of a resin having smaller coefficient of friction than the resilient sealing member. The auxiliary sealing member has a generally identical configuration therewith and is superimposed thereupon with its sealing surfaces 100a lying over respective associated surfaces of the resilient sealing member. The auxiliary sealing member comprises a first sealing portion 101 in the form of an annulus, second sealing portions 102, 102 each in the form of an arc, located at locations diametrically opposite and radially outward of the first sealing portion 101 and extending concentrically therewith, third sealing portions 103, 103, each having an inverted U-shaped configuration and bridging between one end of a corresponding one of the second sealing portions 102, 102 and the first sealing portion 101, and fourth sealing portions 104, 104, each bridging between the other end of the corresponding second sealing portion 102 and the first sealing portion 101.
The control element is rotatable in opposite directions between a minimum capacity position in which the delivery quantity of the compressor is the minimum and a maximum capacity position in which it is the maximum, in response to the difference between the sum of suction pressure as low pressure introduced into the low pressure chamber and the biasing force of a torsion coiled spring, and control pressure Pc created in the high pressure chamber by discharge pressure Pd as high pressure introduced through a restriction into the high pressure chamber. One of the high pressure chambers and a suction chamber in the compressor is communicated with each other via a communication passage across which is arranged a control valve device which opens and closes the communication passage in response to changes in the suction pressure representative of the thermal load, to thereby vary the control pressure and hence the difference between the control pressure and the above-mentioned sum force so that the control element is rotated to vary the timing of commencement of compression and hence the delivery quantity.
Conventional variable capacity vane compressors constructed as above are generally designed to start with the control element in the minimum capacity position in order to reduce starting shock. However, in the above described conventional compressor, the torsion coiled spring which biases the control element in the minimum capacity position has its biasing force preset to such a value as to overcome the rotation resistance of the control element. Consequently, to increase the delivery quantity after the start of the compressor it is necessary to impart to the control element a rotating force which is greater than the sum of the rotation resistance of the control element and the biasing force of the torsion coiled spring. However, at the start of the compressor, the compression ratio is so small that the discharge pressure Pd does not quickly rise and accordingly the control pressure Pc does not quickly rise. Consequently, the control element cannot smoothly rotate in the delivery quantity-increasing direction, resulting in poor startability of the compressor.
Furthermore, the sealing members are rather complicated or three-dimensional in configuration, requiring high precision in manufacturing the control element and hence leading to a high production cost. Besides, the higher the airtightness to be obtained by the sealing means, the higher the seal resistance, which further degrades the compressor startability.